Without a saddle, not having the thing you sit on when riding a horse.
Riding a horse without a saddle might be uncomfortable or unstable.
Examples:
The horse is saddleless, so it feels strange to ride it.
She prefers a saddleless ride because it feels more free.
He rides the saddleless horse with care.
The saddleless horse looks funny without its saddle.
I tried to ride the saddleless horse, but I fell off!
The saddleless horse gallops through the field.